The present invention relates to a visual test system and method for testing the functioning of different parts of the retina and other potions of the visual pathway.
A large number of degenerative eye disorders, such as glaucoma and macular degeneration, may be detected by evaluating a patient""s visual field, such as through perimetry and campimetry. While the patient""s eye is fixated, such visual tests present discrete light stimuli in the patient""s field of vision, and then monitor the patient""s response to the stimuli, allowing a mapping of the visual field to be obtained.
Visual field tests employing test patterns have also been developed for measuring a patient""s visual field. One such visual test uses a so-called xe2x80x9cAmsler gridxe2x80x9d consisting of equally spaced, parallel, horizontal and vertical lines. In use, the grid is positioned about 28-30 cm in front of the patient. With one eye covered, the other eye is fixated on a central point positioned in the grid, such as a dot. The patient is then asked to indicate areas of distortion in the grid by, for example, drawing an outline around the areas of grid distortion, such as, missing squares or wavy lines. Over time, the patient is again asked to note any changes that occur in the severity or location of the grid distortion, typically on a daily or weekly basis.
Visual field tests employing discreet light stimuli, shown one at a time, have been in use and afford accurate thresholding to determine quantitatively the loss of the patient""s visual field. However, such visual tests are very time consuming as well as fatiguing in nature, often requiring the patient to keep his eye fixated for more than 10 minutes. While visual tests employing an Amsler grid are much quicker, thus reducing fatigue, they are generally unable to determine quantitatively the loss of the patient""s visual field.
Recently, a computer-based Amsler grid test has been developed for providing a 3-D depiction of a patient""s visual field. See the press release at www.wfbabcom5.com/wf335.htlm entitled xe2x80x9c3-D Computer-Based Threshold Amsler Grid Test.xe2x80x9d The computerized test displays an Amsler grid at a pre-selected grayscale level and angular resolution on a computer screen positioned a fixed distance from the patient. The patient is then asked to mark areas on the Amsler grid that are missing from his field of vision. This same procedure is then repeated at various contrast levels. The recorded results are then used to display the areas of distortion (X and Y axes) as a function of the visual contrast sensitivity (Z axis). Ostensibly, such a visual field mapping describes the location, extent, slope, depth and shape of the scotomas associated with the loss in the patient""s visual field.
Although no drawbacks are known to the above computerized Amsler grid test, it would still be desirable to have another visual field test which may be capable of more quantitatively, and with greater sensitivity determining a patient""s visual field.
A novel visual field test utilizing oscillating visual stimuli is proposed, which may be used to diagnose for degenerative eye disorders, such as glaucoma or macular degeneration. Such visual stimuli oscillate in color, polarity, saturation, luminance or intensity. Preferably, the visual test pattern consists of oscillating visual stimuli arranged in a pattern, such as a repeating or grid pattern, covering substantially all of the field of vision being tested. Also, frequency doubling visual stimuli may be used, and if desired, the visual stimuli can be caused to move slowly within the patient""s central field of view.
In use, the visual field test pattern is positioned in front of the patient so as to cover substantially all of the field of vision being tested, typically a solid angle of 40xc2x0 or more. The eye under examination is fixated, and the patient asked to indicate areas where the oscillating visual stimuli are dissimilar, such as by outlining those areas different from the rest. This procedure may be repeated for different contrast, saturation or luminance levels, corresponding to varying degrees of visual sensitivity levels. Areas of dissimilarity correspond to visual field defects. The characteristic locations of the areas of dissimilarity for a particular sensitivity setting will allow clinicians not only to diagnose, but also to determine the severity of the eye disorder.
In one embodiment, the visual field test pattern consists of oscillating visual stimuli arranged in a grid pattern. The visual stimuli are located along equally spaced, parallel, horizontal and vertical lines, with a grid spacing of about 1-2 arc minutes. Each visual stimulus has alternating complementary or counter-phase colors oscillating between two complementary or counter phase colors at a frequency fs of about 10-50 Hz.
In another embodiment, the visual field test pattern consists of visual stimuli arranged in a similar grid pattern, but oscillating in polarity between black and white at a frequency of about 10-50 Hz. As above, the eye under examination is fixated, and the patient asked to indicate areas where the visual stimuli for a pre-selected contrast level are dissimilar, such as appearing more gray or unobservable. Alternatively, the visual stimuli can oscillate between intensity levels.
In still another embodiment, the visual field test pattern consists of color frequency doubling visual stimuli similarly arranged in a grid pattern. Each visual stimulus consists of a circular grating pattern having oscillating colors, shown to produce the frequency doubling phenomenon. Although the luminance level remains constant, the color of each grating oscillates preferably between two colors at a frequency fs of about 10-50 times a sec. Alternatively, the visual stimuli can oscillate between saturation or luminance levels.
In another embodiment, the visual field test pattern can consist of a sinusoidal grating pattern having horizontal light and dark bars, contrast modulated at a temporal frequency between 10 and 50 Hz. That is, the bars are contrast modulated in a sinusoidal fashion from white through gray to black at about 10 to 50 times a sec. At such frequencies, the grating pattern is perceived by patients to have double the spatial frequency.
In another embodiment, the light and dark bars can be oriented vertically, instead of horizontally. Furthermore, the grating pattern can be caused to move slowly in a direction at right angles to the lengthwise direction of the grating pattern. In this latter instance, patients would then be asked to identify areas of the visual field test pattern where they fail to observe the direction of movement of the pattern.
Still further, the sinusoidal grating pattern may be alternated between horizontal and vertical, or any two directions. And, the grating pattern need not be contrast modulated in a sinusoidal fashion, but may simply oscillate in polarity between black and white, for example using oscillating dots. Alternatively, a checkerboard pattern oscillating in polarity can also be used.